1. Field of the Invention
The present invention relates to a deflection yoke utilized for a picture displaying apparatus such as a television receiver and a displaying device, which is equipped with a color picture tube, particularly, relates to a deflection yoke being improved on a saddle shaped horizontal deflection coil.
2. Description of the Related Art
In a picture displaying apparatus utilizing a color picture tube of an inline three electron gun type, there existed one method, which utilizes a deflection yoke of self-convergence system, out of several methods for converging three electron beams emitted from three electron guns on a screen or a picture excellently. Such a deflection yoke of self-convergence system is usually composed of a pair of upper and lower saddle shaped horizontal deflection coils and a pair of right and left saddle shaped vertical deflection coils, and then an excellent convergence characteristic can be obtained.
However, a deflection yoke, which was generally mass-produced, generates miss-convergence by reason of scattering of a characteristic of a horizontal or vertical deflection coil and by reason of shifting of a coil allocation when the coil is installed. Accordingly, convergence of almost all deflection coils is adjusted by installing a magnetic piece on an adequate position of a coil, or compensated by a correction circuit.
FIGS. 5(a) and 5(b) show statuses of horizontal deflection magnetic fields unbalanced in right and left.
FIGS. 6(a) and 6(b) show miss-convergence patterns, which generate when a magnetic field is in the statuses shown in FIGS. 5(a) and 5(b). Further, FIGS. 5(a) and 5(b) are cross sectional views of a neck portion 100 of a color picture tube with viewing from a screen side of the color picture tube. In FIGS. 5(a) and 5(b), circled letters xe2x80x9cRxe2x80x9d, xe2x80x9cGxe2x80x9d, and xe2x80x9cBxe2x80x9d represent a cross section of an electron beam of red, green, and blue respectively, curves in a broken line represent magnetic fields, and an arrow xe2x80x9cXxe2x80x9d represents the horizontal direction of the screen. In FIGS. 6(a) and 6(b), letters xe2x80x9cRxe2x80x9d and xe2x80x9cBxe2x80x9d show bright lines drawn by the xe2x80x9cRxe2x80x9d and xe2x80x9cBxe2x80x9d electron beams respectively.
As shown in FIG. 5(a), when a distribution of horizontal deflection magnetic field is unbalanced in right and left, in other words, when a pin cushion of magnetic field for the xe2x80x9cRxe2x80x9d beam is strengthened and a pin cushion of magnetic field for the xe2x80x9cBxe2x80x9d beam is weakened, a miss-convergence happens such that a bright line of the xe2x80x9cRxe2x80x9d shown in a solid line is allocated outside a bright line of the xe2x80x9cBxe2x80x9d shown in a broken line in both the edge areas of the screen in the horizontal direction as shown in FIG. 6(a). On the other hand, as shown in FIG. 5(b), when a pin cushion of magnetic field for the xe2x80x9cRxe2x80x9d beam is weakened and a pin cushion of magnetic field for the xe2x80x9cBxe2x80x9d beam is strengthened, a miss-convergence happens such that a bright line of the xe2x80x9cRxe2x80x9d shown in a solid line is allocated inside a bright line of the xe2x80x9cBxe2x80x9d shown in a broken line in both the edge areas of the screen in the horizontal direction as shown in FIG. 6(b). Such a miss-convergence is called an H-shift miss-convergence.
FIG. 7 is a perspective view of a deflection coil utilized for a deflection yoke of the prior art.
In order to compensate such the miss-convergence mentioned above in a deflection yoke, as shown in FIG. 7, a magnetic piece 26 is allocated on an end surface (toward an electron gun) of each smaller diameter flange 20A (toward an end of neck of a color picture tube) of each horizontal deflection coils 20. It is not mentioned that the magnetic piece 26 is directly adhered on the end surface of each small diameter flange 2A. Generally, the magnetic piece 26 is mounted on a separator. In a case that a magnetic field affecting the xe2x80x9cRxe2x80x9d beam is strong as shown in FIG. 5(a), the magnetic piece 26 is allocated on the left side of the end surface of the smaller diameter flange 20A with viewing from the smaller diameter flange 20A side as shown in FIG. 7. The magnetic piece 26 is magnetized by a magnetic field generated by the smaller diameter flange 20A. Accordingly, the magnetic piece 26 generates a magnetic field of compensating the H-shift miss-convergence.
With referring to FIG. 8, an effect of the magnetic piece 26 will be explained. FIG. 8 is a cross sectional view of a neck portion 100 of a color picture tube with viewing from a screen side of the color picture tube. In FIG. 8, circled letters xe2x80x9cRxe2x80x9d, xe2x80x9cGxe2x80x9d, and xe2x80x9cBxe2x80x9d represent a cross section of an electron beam of red, green, and blue respectively, curves in a broken line represent magnetic fields, and an arrows xe2x80x9cXxe2x80x9d and xe2x80x9cYxe2x80x9d represent the horizontal direction and the vertical direction of the screen respectively. In a case of being deflected toward the left side of the screen, for example, a direction of current flowing through the smaller diameter flange 20A of the horizontal deflection coil 20 is shown by an arrow 210. The magnetic piece 26, which is allocated closer to the electron gun than the smaller diameter flange 20A, is magnetized with being oriented to an arrow 230 by a magnetic field generated by the smaller diameter flange 20A within a range of broken line 220.
A magnetic field generated by the magnetic piece 26, as a result of being magnetized, is oriented toward a direction of canceling a main deflection magnetic field generated by the horizontal deflection coil 20, that is, toward a direction of weakening the magnetic field in the right side of the neck portion 100 and unbalanced magnetic field in right and left is solved. Accordingly, the magnetic piece 26 is magnetized by the magnetic field in the xe2x80x9cYxe2x80x9d direction generated by the smaller diameter flange 20A, and then the H-shift miss-convergence is compensated by the magnetic field generated by the magnetic piece 26 being magnetized.
A degree of influence on a convergence characteristic caused by variations of the horizontal deflection coil 20 and dislocation of the horizontal deflection coil 20 during installation is increasing in response to recent trend toward a larger screen of a displaying device. Further, demand for decreasing a deflection power of a deflection yoke is increasing for the purpose of power saving of a displaying device. In order to match the trend and demand, as disclosed in the Japanese Patent Laid-open Publication No. 8-153477, for example, the smaller diameter flange 20A of the horizontal deflection coil 20 tends to be miniaturized. The magnetic field of the smaller diameter flange 20A, which magnetizes the magnetic piece 26, decreases as a result of a miniaturized smaller diameter flange. Accordingly, an effect of compensating the H-shift miss-convergence is deteriorated.
In order to increase the effect of compensating the H-shift miss-convergence, dimensions of the magnetic piece 26 shall be enlarged. However, the magnetic piece 26 is generally made of formed ferrite, so that a manufacturing cost of the magnetic piece 26 increases if the dimension is enlarged. Further, since a coil for compensating coma is mounted on a smaller diameter flange of a separator for a deflection yoke and some components such as a fastening band for fastening a cylindrical neck portion provided on the smaller diameter flange to a neck portion of a color picture tube are mounted on the cylindrical neck portion, enlarging the dimensions of the magnetic piece 26 is inevitably limited by a mounting construction and a mounting allocation.
Accordingly, in consideration of the above-mentioned problems of the prior art, an object of the present invention is to provide a deflection yoke, which can effectively compensate the H-shift miss-convergence without enlarging dimensions of a magnetic piece for compensating the H-shift miss-convergence.
In order to achieve the above object, the present invention provides, according to an aspect thereof, a deflection yoke being mounted on a neck portion of a color picture tube comprising a pair of horizontal deflection coils, which are composed of a smaller diameter side toward the neck portion and a larger diameter side toward a screen side of the color picture tube, having a flange on the smaller diameter side, wherein a width of the flange in a horizontal direction of the screen is more than twice a height of the flange in a vertical direction of the screen.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.